The present invention relates to a method of treating liquid waste (liquid agricultural or industrial effluents or aquatic sites) loaded or polluted with tributyl phosphate (TBP), to modified bacterial strains which can be used in said treatment method, to a method of monitoring changes in TBP pollution, and to a device which is used to carry out said treatment method.
Tributyl phosphate (TBP) is an organophosphorus compound used in many industrial fields, and in particular: as a solvent in the recycling of nuclear fuel and in the purification of rare metals or in the manufacture of plasticizers, hydraulic fluids, pesticides, herbicides, antifoaming agents or anticorrosive agents.
All these applications generate large amounts of waste, which is relatively non-biodegradable, since TBP is barely degraded or not at all, in a natural environment: it is barely degraded by indigenous microorganisms and it is relatively insensitive to photolysis or to natural hydrolysis.
Although TBP is not toxic to the human organism, it is nonetheless toxic with respect to various aquatic organisms (trout, shrimp, algae, bacteria), which can result in an ecological imbalance at the contaminated sites.
Documents exist that disclose general methods of degrading organic compounds in liquid effluents:                U.S. Pat. No. 6,472,198 discloses the degradation of chlorinated organic compounds using indigenous bacteria, in particular of methanogenic or acetogenic type, or bacteria responsible for the dehalogenation or denitrification, these bacteria functioning under conditions of aerobiosis or anaerobiosis. Such a method is not suitable for the degradation of TBP.        U.S. Pat. No. 6,106,719, discloses the use, for the treatment of liquid waste containing both organic compounds and inorganic compounds containing nitrogen or phosphorus, of a combination of bacteria in the form of solid granules, under conditions of anaerobiosis and in the presence of light; said combination of bacteria comprises (a) a mixture of non-photosynthetic bacteria: acid fermentation bacteria and/or methane-producing bacteria, and (b) a mixture of photosynthetic bacteria (purple non-sulfur bacteria, purple sulfur bacteria and green sulfur bacteria, such as Chrorobium limicola, Chromatium vinosum, Rhodopseudomonas palustris or Rhodobacter capsulatus). Such a treatment makes it possible to digest the organic material, and to digest the inorganic compounds comprising nitrogen and/or phosphorus. In the method disclosed in that patent, the disappearance of the inorganic phosphorus is linked to the growth of the photosynthetic bacteria. Such a method is not therefore suitable for the treatment of TBP.        U.S. Pat. Nos. 6,416,993 and 6,465,240 disclose a method of degrading liquid organic and inorganic waste, which comprises two steps of treatment with photosynthetic microorganisms: a first treatment with one or more photosynthetic prokaryote(s) and, preferably, a consortium of photosynthetic bacteria (purple non-sulfur bacteria: Rhodospirillum, Rhodopseudomonas, Rhodobacter, Chromatium, Rubrivivax or cyanobacteria), and then a second treatment with photosynthetic algae. More specifically, said method disclosed makes it possible to treat waste containing high concentrations of total organic carbon (TOC), of biochemical oxygen demand (BOD), of nitrogen (including aqueous ammonia) and of phosphorus (P, including phosphates, polyphosphates, organic phosphates) and also other organic or inorganic substances. However, these methods are not suitable for the degradation of TBP, which may be present at high concentrations (of the order of 100 mg/ml); in fact, the methods disclosed in those two patents apply to the treatment of agricultural effluents, such as liquid manure, in which little or no TBP is found. In addition, TBP is reputed to be toxic for bacteria and algae at low concentrations (Nakamura A., 1991, International Program on Chemical Safety-Environmental Health Critiria 112-Tri-n-Butyl Phosphate QV 627. World Health Organisation).        
The methods of the prior art that are aimed at the treatment of all organic and inorganic products are not therefore suitable for the treatment of waste comprising TBP, since the growth of the algae and of the nonphotosynthetic bacteria used is generally inhibited by TBP.
The degradation of TBP by microorganisms has been the subject of few studies; it generally uses microorganisms that act under conditions of aerobiosis:                U.S. Pat. No. 5,453,375 discloses a method of degrading TBP which uses the bacterial strain Acinetobacter sp., under conditions of aerobiosis.        In other studies, the team of R. A. Thomas et al. [1, 2, 3, 4] has disclosed the use of a mixture of microorganisms of the genus Pseudomonas spp., for degrading TBP under conditions of aerobiosis.        In the article by S. Owen et al. [5], the use of Citrobacter sp. bacteria is recommended under conditions of aerobiosis for degrading TBP.        
The conditions (aerobiosis) disclosed in those documents have the following drawbacks:                low TBP degradation yield,        random method reproducibility.        
Consequently, all the methods of treating organic waste recommended in the prior art are therefore unsuitable for the treatment of TBP, insofar as none of them discloses a method that is at the same time stable, reproducible, effective and high-yield (>400 mg/l) for degrading TBP, present in varying concentration ranges.
Consequently, the Applicant has given itself the aim of providing a method of treating liquid waste containing TBP, which better satisfies the practical needs than the methods of the prior art, in particular in that it effectively makes it possible to degrade TBP, with a good yield and in particular, under certain conditions, a yield greater than 400 mg/l, while at the same time being reproducible.